Carburetor



Jan. 15, 1929. 1,698,856

W. B. RALSTQN summon Filed Nov. 18., 1220 2 Sheetra-8heot i1.

INVENTOR. I 83 Y A TTORNEYQ olnii Jan. 15, 1929.

W. B. RALSTON CARBURETOR 2, Sheets-Sheet 2 Filed Nov. 18. 1920 INVENTOR.

A TTORNE Y.

Oil

Patented Jan. 15, 1929.

UNITED STATES WILLIAM B. RALSTON, 015 FORT WAYNE, INDIANA.

CARIBURETOR.

Application filed November This invention relates to improvementsin carburetors, for hydrocarbon engines, of a character similar to that set forth in my previous application, Sr. No. 383,120, now Pat ent No. 1,679,742, of Aug. 7, 1928, for carburetors. The object of the present invention is to afford an improved construction for automatically regulating the admission of gasoline into the mixing chamber according to the volume of air admitted, in such manner to facilitate the effectiveness in opera-- tien of the engine at low speed and economy in its consumption of fuel at high speed and a further object to provide means of adjustment of the air'admission mechanism so as to vary the action of the gasoline admission mechanism.

These objects of the improvements are accomplished by the construction illustrated in the accompanying drawings in which:

Fig. .1 is a vertical central section of a carburetor embodying the invention and applied in connection with the exhaust and intake manifolds of an engine;

Fig. 2 is a plan view of the same upon a reduced scale;

Fig. 3 is a detail view showing a vertical section of the mixing chamber in a plane extending centrally through the secondary air inlet port;

Fig. 4 is a front elevation of the deylcc;

Fig. 5 is a side elevation of the ad ustable fulcrum;

Fig. 6 is an end View of the same;

Fig. 7 is a detail view showing a front elevation of a portion of the device including the gasoline valves and appurtenances thereto, the view being taken from the left n Fig. 1 and shown partially broken away and in section; and

Fig. 8 is a plan view of the air inlet valve.

Similar characters of reference indicate corresponding parts throughout the several views. and referring now to the same: i

1 is the exhaust manifold of an internal combustion engine and 2 is the intake manifold thereof. 3 is a casting forming the body ,of the carburetor, which is provided with a projecting cylindrical extension 4 at one end thereof and has a mixing chamber 5 with an outlet duct- 6 leading dowiiwardlyrtherefrom into the intake manifold, there being a throt tle valve 7 arranged in the duct. The extension 4 of the body, in which is located part of the mixing chamber, projects through an 18, 1920. Serial No. 424,826.

opening 8 in the exhaust manifold into the interior thereof directly in the path of the exhaust so as to become heated thereby. In the top' of the body casting is a chamber 9 that has communication with the mixing chamber 5 through a valve opening 10. A chambered inlet member 11 is mounted on the body and has communication with the receiving chamber 9 through an inlet port 12 which is normally approximately closed by an air inlet valve 13, the arrangement being such as to provide permanent communication between the inlet 11 and chamber 9. Hence, chamber 9 is permanently open to atmospheric pressure, even though valve 13 is in its upper position and at the upper limit of its movement, the arrangement, as in the companion application, Serial No. 383,120,

(Patent No. 1,679,742) heretofore referred to, serving to permit admission of air to chamber 9, although, in this position, the area of the communicating opening may be relatively small as compared with opening 12. As presently described, this permits of the development of a differential in pressure values between chamber 9whicl1 may be termed an entry chamber-and the mixing chamber 5, as in the companion application referred to. A hollow post 14 is rigidly positioned in the inlet member 11 in alinement .with the centers of the port 12 and Valve opening 10, and the valve 13 is provided with a hollow stem 15 at the upper end of which is'a piston head 16 sliding loosel on the post. The air inlet member 11 has formed in its upper part a dash pot chamber l7'shapedto receive the piston head 16, the purpose of which piston head and dash pot chamber is to stabilize movements of the air inlet valve 13. The lower end of the post 14 is enlarged so as to support a compression spring 18 thereon, and the upper end of the spring bears against the piston head 16 and tends to hold the valve 13 in its approximately closed position. The valve 13 has a series of wings 19 extending in the inlet port 12 which serve as guides. Fit-ting loosely in the opening 10 "is a secondary air valve 20 having a hollow":

stem 21 that extends loosely within the stem 15 of the air valve 13 and is vertically movable therein and is provided with'an-i'nternal flange 22 adapted to be engaged by the-lower end of the hollow p0st 14 so that the upward movement of the secondary valve is thereby limited. A vertically adjustable rod 23 extends downwardly through the hollow post into the lower part of the stem 21 of valve and has an enlarged lower end 24 that afon the stem of the secondary valve and an. arrester 27 on the air valve 13 by which downward movement of the secondary valve 20 relative to valve 13 is limited. It is the intention that the action of the secondary valve shall be more sensitive than that of the air valve and the spring for supporting the 1 secondary valve is therefore weaker thanthe chamber.

spring 18 that supports the air valve. On the top of the inlet member 11 is a projecting boss 28 upon whichis mounted an arm 29 having a sleeve 30, the latter fitting over the boss and being provided with opposite cam slots 31 through which corresponding screw pins 32 extend into the boss so that as the arm is turned it moves vertically causing the spring 25 to be compressed accordingly.

The chamber 5- is closed at-its front end by a head 33 which has a pipe 34 that projects centrally into the chamber and terminates near the inner end thereof with a flaring flange 35 having a back turned rim 36, there being a space 37 between the flange and the adjacent end wall 38 of the chamber and between the rim 36 and the surrounding wall 39 of the chamber sufficient to admit the passage of fuel from the pipe into the mixing The pipe 34 has also extending from each side thereofa partition 34' that divides the mixing chamber 5-horizontally from the front end thereof to a point near the rim 36. The head has a hollow stem 40 part movement from the secondary air-valve to the needle valve, there being a nut 47 for adjusting the fulcrum. a

The lower end of the stem 40 has a chamber 49'therein which is supplied with liquid fuel from a float chamber 50 connected therewith and in the stem is formed a by-pass duct may be independentlyintroduced into the pipe 34 to'augment the amount drawn thereinto from the nozzle.

Onone side of the stem 40 is arranged a' sliding member 53 which has a lug-54 that projects into the stem and is adapted to engage the collar 44 when moved upwardly and lift the needle valve 43.

The float chamber 50 may be of any suitable construction for supplying liquid fuel to the chamber 49 in the lower part of the stem 40, and is preferably provided with a lug 55 forits support on the head 33, there being a block 56 of heat insulating material interposed between the lug and the head adapted to prevent the float chamber from becoming excessively heated by absorption through its support. 1

It is the intention. especially when the carburetor is employed in an automobile, to provide for the operation of the lever 29, slide and by-pass valve 52 from a point within convenient reach of the operator, in view of which the lever 29 has a control wire 57 the slide 53 has a similar wire 58 and the valve 52 has a rod 59, each of which may be ary ranged for their manipulation from any suitable remote point as may be desired.

In the operation of the invention the liquid fuel passing outof the nozzle 42 becomes atomized and is drawn with air admitted through the air inlet openings 41 through the pipe 34 and against the heated walls of the cylind i- ,cal extension into the mixing chamber 5. As the mixture thus formed is drawn through the narrow space 37 between the flange and end wall and the wall surrounding the rim 36, all of the atomized liquid is thus brought into close proximity to the walls of the extension which are heated by the exhaust from the engine passing through the exhaust manifold, and thereby becomes vaporized in its passage from the pipe into the mixing chamber.

The chamber 9which may be termed an entry cha1nber-has the characteristic of having its air content at a lower pressure than atmospheric pressure and a pressure higher than the pressure in the mixing chamber, excepting when the engine is at rest, when both chambers are at atmospheric pressure. This.

is due to the fact that valve 13, when seated,

does not completely close the port 12, so that air can flow into chamber 9 from the intake 11 at'all'times; hence, any depression in chamber 9 which is produced by bringing this chamber into communication with the mixing chamber by opening valve 20, produces a differential in pressure across valve 13 and causes air to flow into chamber 9 as leakage around valve 13, and thus prevent the pressure in chamber 9 from reaching the degree of lowered pressure present in the mixing chamber. The differential in pressure between the atmospheric and mixing chamber is therefore divided into a two-stage development, with the pressure of the air in chamber 9 forming the low'of the differential in pressure across valve 13, and the high of the differential in pressure across valve 20, the

IOU

, total of the differential in pressure across these valves, being equal to the differential in pressure between the atmosphere and the mixin chamber.

'lhese conditions are of importance in the operation of the carburetor, as will be understood from a brief description of various phases of service operation. When the carburetor is idle, both valves 13 and 20 will be seated through the action of their springs 18 and 25, respectively; communication between the entry and mixing chambers is closed by the location of valve 20 in its closed position, while the entry chamber is in leakage communication with the atmosphere around valve 13. The mixing chamber is in communication with the atmosphere through port 41 and the passage 34, thus placing both chambers at atmospheric pressure. At this time the fuel valve 43 is closed, since valve 20 is in its upper position, and spring 45 is active to hold the fuel valve to its seat.

When throttle valve 7 is opened and the engine turning over, the pressure in mixing chamber 5 is lowered, producing a differential in pressure across valve 20. As long as arrester 27 and flange 26 remain out of contact, the resistance of valve 20 is determinedby the power of" spring 25which is a light spring and therefore responsive to small variations in pressure differentials; hence, the lowering in pressure in theamixing chamber will cause valve 20 to open Whenever the dif ferential across the valve equals or exceeds the power of spring 25, thus opening communication between the-two chambers and reducing the pressure in the entry chamber because of the communication between the chambers, the

pressure drop in the entry chamber, however, not equalling that of the mixing chamher, due to the feeding of air around valve 13, as heretofore painted out. The movement of valve 20, in response to this development, serves to move fuel valve 43 to open the latter, the length of movement being dependent on the length of movement of valve 20.

In this particular stage of the developmentthe stage-during which flange 26 and the arrester 27 are out of contact-valve 20 is sensitive to variations in the pressure of the mixing chamber, so that the conditions present provide for efiicient operation during the idlingoperations of the engine, since valve 20, because of its scnsitiveness. will detect small changes in pressure of the mixing chamber, and the responsive movements of valve 20 will produce corresponding movements of the fuel valve to enable a proper compensation in fuel supply during the stage. The, fuel requirements. during the idling period,

are small, and the ability to provide the proper compensation in presence of pressure changes is of great advantage.

This is madepossible by the conditions,

present in. entry chamber 9. As will be understood, valve 13, which is held to its seat by the more powerful spring 18, will not move from its seat until the differential in pressure across Valve 13 is sufficient to overcome the power of spring 18; but this does not prevent the differential across valve 13 from varying, while the valve remains seated, such variations in differential in pressure simply causing variations in the velocity of 'flow of air around valve 13. Hence, variations in pressure in the mixing chamber during this stage do not affect the sensitiveness of valve '20, since the pressure in the entry chamber drops correspondingly, due to the fact that the differential across valve 20 is controlled entirely by the power of spring 25, the variations in power being small since they are determined by the compression of the spring itself. In other words, the value of the differential across valve 20 remains approximately constant, while that across valve 13 varies approximately equal to the variations in the pressure in the mixing cham "er, after differential conditions across the va ves have been produced by the opening of the throttle. Because of this, the 'sensitiveness'of valve 20- and the corresponding sensitiveness of fuel valve 43is maintained approximately constant, as long as the fluctuations in pressure in the mixing chamber do not reach apoint; where the movement of valve '20 establishes contact between flange 26 and the arrester 27' while responding to these pressure variations in the mixing chamber. These conditions remain during the period of lost m0tion present'in the movements of flange 26 relative to arrester 27, and are changed only when such lost motion condition is absent by reason of contact between the flange and arrester.

A change in the conditions takes placewhen flange 26 and the arrester are brought into contact. Valve 20is still free to move upward (in Fig. '1) to break the contact,

whenever the pressure in the mixing chamber is raised sufficiently to decrease the differential across 'valve 20 to a value less than the power of spring 25; but the. movement of valve 20 downward (in Fig. 1) after such contact is had, is made under different conditions. Since the arrcster must move with the flange to continuc'the downward movement of valve 20. it will be readily understood that such continued movement of valve 20 can take place only when valve 13 moves with it, due to the fact that the arrester is carried by valve 13; hence. the power of spring 18 supplements the power of spring 25 as a resistance to the movement of valve 20 in the downwardidirectionspring 25 does not materially increase the resistance to movement of valve 20 in this direction while spring 18 is acting as the re:i(stanc}e for valve 20, but is constantly activ duri g this period as a power source capable of breaking the contact between the flange and arrester upon do.

across valve 13 equal to or greater than the power of spring 18; and. since the high 'of this differential (the atmosphere) does not change, the change must be through changing the low of the differential, this being socured by lowering the pressure in the entry chamber. And since the pressure of that chamber is also the high of the differential in pressure across valve 20, it will be readily understood that movement of valve 13 from its seat can be had only by changing the low of the differential across valve 20 by lowering the pressure in the mixing chamber.

In other words, the differential in pressure between the atmosphere and the mixing chamber cannot be less than that required to overcome the power of spring 18, in order that valve 13 may move from its seat; this differential is divided into ,two stages, as

before, but the pressure in the'entry cham-' ber has now become considerably lowered through the fact that it must form the low of the differential in pressure across valve 13.

As such changes are brought about by throttle manipulation, it will be understood that the opening of the throttle to increase the speed, will quickly develop the ncreased pressure drop in the mixing chamber and, through the latter, the required pressure drop in the entry chamber, whenever the throttle movement is such as to require unseatlng of valve 13 to supply the air increments needed. There. is a considerable difference in the power of the two springs 18 and 25, and the change which places spring 18 as the resistance to movement of valve 20 necessitates the rapid developmentof the needed pressure drop in the two chambers. Since valve 13 will remain seated until the pressure drop in the entry chamber is had, and port 41 is of constant area, it ivill be understood that the suction increase provided by the opening of the throttle, will quickly produce the de-' sired change in the conditions in the mixing chamber and the resultant. change in the pressure in the entry chamber.

In this development, the position of valves 20 and 43 is not changed until valve 13 begins to unseat. But a resultant effect on the fuel supply is made manifest during the period. This is due to the fact that as the pressure lowers in the mixing chamber it has the effect of increasing thedifferential in pressureat the opposite ends of port 41', with the result that the velocity of the air entering this port is also rapidly increased;

with the increase in air velocity at the fuel outlet, the fuel drawn will be of increased amount, and this will be carried onward with the increase in velocity of the air, thus delivering to the mixing chamber a greater 7P amount of fuel per unit of time, the increase being progressive as the differential in pressureat port 41 increases. As a result, the failure to change the position of the fuel valve 43 during this period of development of the pressure drop in the mixing chamber when changing from the resistance of spring 25 to that of spring 18, does not prevent increasing the supply of fuel to meet the changing conditionsany material delay in the development of the pressure drop to the point where valve 13 begins to unseat, could only tend to increase the richness of the charge in the mixing chamber, through the action set up by the increase in air velocity at 8 the fuel outlet; and the richer charge during this period is of advantage, since it helps in. changing the speed of the engine itself; with the opening of valve 13, the temporary .en-

richment would be changed bythe greateri amount of air being delivered through the air supplied from the entry chamber. The structure thus provides for efficient action during the period in which the resistance to movement of valve 20 is changed from spring 25 to spring 18.

With the pressure drop in the mixing chamber sufficient to develop the differential in pressure across valve 13 such as to cause the valve to unseat, valve 20 will move with valve 13, so far as further downward movement of valve 20 is concerned, the lowerpower spring 25 being insufficient to break the contact between the flange and arrester,

excepting under certain conditions presently referred to such movements of the two valves,however, will be under the restraint action of the dash pot structure 16, 17. And it will be understood-that with the two valves thus coupled for operation, further opening of the throttle will increase the pressure drop in the mixing chamber with its correspoiiding change in the entry chamber to increase the differential across valve 13, and, thereby cause further 0 ening movements of the two valves, valve 4., also partaking of these movements because of the movement of valve 2Q, and thus opening the fuel outlet accordingly. The operation of the carburetor, in this second stage of the development-the stage in which spring 18 is acting as the resistance for valve 20-1s thus generally similar to that gof the first stageof the development, so far now placed on spring 18, it will be understood 7 that an lncrement of pressure drop which no would be restored after this period of inde-- pendentmovement, since the several movements of this valve would produce conditions in the entry chamber such as to place the pressure of the latter sufliciently above that of the mixing chamber as to produce the differential across valve 13 needed to retain the latter in its new position, and at the same 7 time restore the contact of flange and arrester so as to place valve 20 again under the control of spring 18 so far as movement downward is concerned; When the closing movement of the'throttle is such to produce conditions in which the valve 13 moves to its seated positionthus settingiup the characteristics of the first stage operationthe contact of flange and arrester may not be restored in passing from one stage to the other.

While these movements of valve 20 in this stage have an effect in the control of the pressure in the entry chamber, an important effect produced is in the supply of fuel. This results from the fact that the pressure rise in the mixing chamber reduces the differential at the port 41, and therefore reduces the velocity of the flow of air passing the fuel outlet, while the upward movement of valve 20 per mits spring 45 to shift the fuel valve toward its closing position, thus affecting the supply of fuel rapidly and efliciently. Since the purpose of the movement of the throttle in the closing direction is to reduce-the speed,

- this immediate response of a rapid reduction in the fuel supply is of material importance. If the change produced by the throttle move ment still leaves the valve 13 unseated, the downward movement of valve'20 in again restoring the contact of flange and arrester, produces an opening movement of valve 43, as in the first stage operation, until the contact of flangeand arrester again produces the conditions of the second stage operation with respect to the fuel valve, whereupon the car buretor continues its operation under the conditions produced by the shifting of the throttle;

As will beseen, therefore, the structure not only provides for operation in which the fuel charge is leaned during the higher speed operations, but also that the responses made to change in position of the throttle are not only rapid and immediate, but are so developed as to aid in completing the change in operation which the throttle operation is designed to produce; with the throttle moved to increase the speed, the charge is temporaril enriched as to fuel content, andwhen the c iange is lI1 '-,th8 direction of a reduction in speed, the charge is temporarily leaned, both of these conditions aiding in the rapid development of the end desired by the movesuch pressure, and also during the pressure drop conditions of the first stage when the differential in pressure at port 41 is relatively small and the air velocity changes are less able to vary the fuel supply-during such latter period, the fuel valve is very sensitive to the pressure variations in the fuelcham- 1581' through the movements of sensitive valve The lost-motion connection between valves 13 and 20 is, limited in its extent by: the flange 26 and by theend of the valve hub,

since either one or the other will contact with the arrester flange when valve 20 is sufliciently shifted, flange 26 becoming active in this respect when beyond the idling speed, while the hub end may become active only occasionally. Obviously, this condition remains when valve 13 is unseated, the movement of the latter valve simply shifting the position of the flange of the arrester with which the flange 26 and hub end may contact to-limit the independentmovement of valve 20 within the lost motion limits.

The air admitted to the mixin through the inlet member the partitions toward the chamber and there unites with the entering mixture of vaporized fuel and air preparatory to its passage to the intake manifold.

By manipulating the nut 47 the fulcrum chamber 11 is diverted by heated end of the 46 may be adjustably shifted so that the op- .eration of the lever 48 .will correspondingly effect the operation of the needle valve. By manipulating the control wire 57, the arm 29 may be turned so as to reduce the stress of the spring 25 which willpermit the secondary valve to respond more freely to the action of the indraft of air admitted by the air valve and the needle valve will thereby be actuated with greater sensitiveness, and the flow of gasoline increased.

\Vhen a greater quantity of liquid fuel is required than that admitted through the noz zle, as during the initial operation of the engine, when cold, the I itional fuel may be suppliedby openin the y-pass valve 52 so as to augment the amount drawn through the nozzle. Also, a priming charge of gasowould move valve 20 downward for a unit of distance during the first stage, will cause such valve movement for but a fraction of this distance in the second stage, due to'the factthat the power of resistance to movement of the valve has been increased. In other words, to'move the valve 20 downward a unit of distance under the changed conditions, requires a larger increment of pressure drop than is required in the first stage operation. And since the opening movement of valve 43 is in correspondence 'with the movement of valve 20, the same changed condition is present in the response of valve 43 to the development of the pressure drop in the mixing chamber. Obviously, these conditions materially reduce the sensitiveness of valve 20 in connection with valve movements downward, a condition which; is increased through the presence-of the dash-pot structure.

This change in responsiveness of valve 43- the change'which reducesthe length of the increment of valve movement per unit of pressure drop-has an eifect in the supply of the fuel, the proportion of fuel to air being changed so that, as the speed is increased, the mixture is leaned proportionately. Th s change, however, is not ,completed by this change in length of movement of valve 43; the change in responsiveness of valve 43 to variations in pressure could disturb the smoothness of operation if dependence were placed on this alone. As heretofore pointed out, change in the differential in pressure at the opposite ends of port 41 occurs when pressure is reduced in the mixing chamber, and since this condition is present with greater effect during this second stage development, it will be understood that the increase in velocity of the air flow past the fuel outlet,

provides a' compensating efiect in that the fuel supply is controlled not only by the position of the fuel valve but also by the action of velocity variations in the flow of air admitted through port 41; this double control tends to overcome the difiiculties that are inherently present whenever the attempt is made to vary the fuel supply by comparatively small changes in the position of a mechanically-operated valve.

\Vithin this second stage operation, however, the operation is varied from that of the first stage when the movement of the throttle is in a closing direction, due to the fact that the variation in pressure within the mixing chamber is in the direction of a pressure rise. Such throttle change takes place generally to end a steady running condition in which the position of the unseated valve 13 and the valve 20 is more or less valve 13 is sufficient to balance the power of sistance of spring 25, valve 20 at such time being projected within the mixing chamber to such an extent as to permit free flow of air from the entry chamber, so that the differential across valve 20 need not exceed that needed to preserve the contact between flange 26 and the arrester.

When, therefore, the throttle is moved in its' closing direction, with the resulting effect of reducing the movement of the charge from the mixing'chamber, the immediate response to the action is a rise in the pressure of the mixing chamber. This is due to the fact that not only is the demand lessened by the throttle movement, but, in addition, the dash-pot prevents a snap return of valve 13 in the direction of its'seat, so that there is a lag in reducing the area of the port'which feeds the entry chamber; as a result, the pressure rise in the mixing chamber is the resultant of a lessening of the demand while feeding an excess amount of air, thus building the rise rapidly. As a result, the power of spring 1-8 becomes dominant to move valve 13 toward its seat but such movement is subject to the dashpot action. But a further result is produced because'of the reduction of the differential in pressure across valve 20; this reduction in differential renders the power of spring 25 dominant, with the result that valve 20 is moved upward in Fig. 1 not only through the action of the arrester, but is moved more rapi-dly than the latter by reason of the independent activity of spring 25, so that flange 26 is moved out of contact with the arresterthe lost motion relation permit-ting this to take place. This independent movement of such that valve 20 could not reach the position shown in Fig. 1, it :will be understood that such movement of valve 20 could-cont-inue until the inner endof the hub flange of the valve would contact with the 'arrester flange.

. The extent of such independent movement of valve 20 will depend upon the relative pressures of the entryfand mixing chambers.

Since the closing movement of valve 20 decreases the area. of the opening between the chambers through which the air is being fed, a point is reached where the'pressure rise in the entry chamber is more rapid than that in the mixing chamber, with the resu'lt'ithat the differential across the valve also rises. and

becomes equal to that of the power of spring 25, at which time the valve 20 again becomes any time become ignited by back-lire from the engine, the pressure in the mixing chamber occasioned thereby causes both the air valve and secondary valve to move upwardly and close their respective openings, forming a double check which prevents the flame from escaping through the air inlet, and owing to the narrowness of the space 37 about the flange 35 and its rim, the flame becomes choked and extinguished therein as the pressure is relieved back through the pipe 34.

From the above it will be understood that, in operation, the structure provides for subjecting the opposite sides of the detectmg valve to the conditions of adifferential in pressures (with the low of the dlflerential provided by the pressure of the mixing chamber), with the diflerential conditions so arranged as to provide for more than one standard of differential value-two of these standards being employed, one being that set up by the resistance of spring 25 alone, the other by the combined action of the resistance of springs 25 and 18. Each standard is variable through the change in resistance value of the a springs brought about by the variations in compression of the springs, this variation being within the zone of activity of the general standard of the zone. As will be understood, one of these standards is active during the period when flange 26 and arrester 27 are'out of contact, the other standard being active when these are in contact. Hence, during service conditions within the minimum and maximum speed limits of the engine being served, both standards may be made active, but the activity of the standards is non-concurrent; since any change in standard during service operation is from one to the other, it will be understood that during operating conditions where both are brought into activitylow and high speed activity--the change from one-to--the other sets up the con- .ditions of successive activity as between the standards.-

As a resultant effect, the fuel valve 43 has its movements based on two difl'erent rates of progression movement, the rate of movement during the period when flange 26 and arrester 27-are out of contact, being higher than when these are in contact; This will be understood from the fact that in producing an increment of movement of valve 43 of a definite length by the movement of the detector valve 20, the drop in pressure within the mixing chamber required is greater with both springs active than :where spring 25 alone active, valve 20 being required to move the same distance in producing the increment of fuel valve movement in both cases. Hence, for equal increments in drop of pressure in the mixing. chamber, the rate of progression movement during the period when spring 25 alone is active, will be greater than when both springs are active. As before pointed out, compensating action is provided by the change in conditions at the entrance to the initial mixture passageway, due to the change in the conditions in the mixing chamber set up by the use of a different low for the differential present in connection with valve 20 when the change in standard of differential is provided.

\Vhat I claim is:

1. A carburetor having a fuel inlet and a valve for said inlet; an air inlet; a suctionoperated valve obstructing but not closing tightly said air inlet; a second suction-operated valve closing said air inlet between the named valve and the fuel inlet and arranged to open at a lower suction than the firstnamed/valve; means to transmit motion from said second air valve to the fuel valve, and a lost-motion connection, between said air valves permitting the second valve to have a movement between limits independent of the fuel inlet 'and a valve therefor, a mixing chamber;an air inlet, apair of suction-operated valves arranged serially in the flow path of air through the air inlet to the mixing chamber, said pair of valves serving to provide an entry chamber between the mixing chamber'and the'atmosphere, the outer of the valves of the pair obstructing but not closing tightly the air inlet to the entry chamber and the inner valve of the pair controlling the passage of air from the entry chamber to the mixin chamber and being arranged to open at a lower suction than the outer valve, and mechanism for transmitting motion of the inner valve to the fuel valve, of means for operatively connecting the pair of valves, said means permitting the inner valve to have movement between limits independent of the outer valve but causing said valves to move together beyond said limits.

In testimony whereof I aifix my si nature.

WILLIAM B. ALsroN. 

